\begin{tikzpicture}[>=Stealth]
    \node at (0, 0) {$a$};
    \node at (1, 0) {$b$};
    \node at (2, 0) {$c$};
    \node at (3, 0) {$d$};
    \draw [->] (0, -0.2) arc(240:300:1);
    \draw [->] (0, -0.2) arc(240:300:2);
    \draw [->] (0, -0.2) arc(240:300:3);


    \node at (5, 0) {$b$};
    \node at (6, 0) {$c$};
    \node at (7, 0) {$d$};
    \draw [->] (5, -0.2) arc(240:300:1);
    \draw [->] (5, -0.2) arc(240:300:2);

    \node at (9, 0) {$c$};
    \node at (10, 0) {$d$};
    \draw [->] (9, -0.2) arc(240:300:1);
\end{tikzpicture}
